One type of semiconductor package is referred to as a ball grid array (BGA) package. BGA packages were developed to provide a higher lead count and a smaller foot print as compared to conventional plastic or ceramic semiconductor packages. A BGA package includes an area array of solder balls that permit the package to be surface mounted to a printed circuit board (PCB) or other electronic component.
A conventional BGA package includes a planar dielectric substrate, a semiconductor die mounted to the substrate using a die attach material (e.g., a paste), and an encapsulating epoxy resin which encapsulates the die. The substrate is initially a segment of a substrate panel (or sheet). The substrate panel includes multiple substrates that is used to simultaneously fabricate multiple BGA packages. Following the fabrication process for the BGA packages, the substrate panel is singulated into individual BGA package devices.
Typically, the substrate comprises a reinforced polymer laminate material, such as bismaleimide triazine (BT), or a polyimide resin. The substrate includes a planar die attach surface that generally comprises a dielectric solder resist layer on a metal layer (e.g., copper). During a die attach step of the assembly process, the semiconductor die is adhesively bonded to a planar solder resist layer on the substrate using a die attach adhesive. The semiconductor die is then bonded to bond pads on the substrate that are revealed by apertures in the solder resist layer.
Another type of package substrate is a lead frame that is generally processed as a lead frame sheet. For lead frames the die pad is generally flat and comprises a metal and a plurality of metal lead fingers are around the die pad.
Both dielectric substrates for BGA packages and lead frames for lead frame-based devices are subject to problems associated with the inability to control the volume of die attach material either under the semiconductor die in the case of under dispense, or lateral to the semiconductor die in the case of over dispense. Such inability to control the volume of the die attach material in the case of wirebonding assembly can result in wire bond failures between the semiconductor die and pads on a package substrate or the lead fingers of a lead frame.